Taliban fighters have taken over a police headquarters in Afghanistan's western Farah province during an ongoing battle with the security forces as officials warned the district was likely to be taken over by the armed group.

At least 20 members of the security forces are believed to be killed or wounded when the fighters attacked the Anar Dara district's police and administrative offices on Monday morning.

The exact number of killed or wounded is still not clear as the fighting is still under way, officials said.

"The [Taliban] fighters attacked the district offices early in the morning from different directions and have taken over the offices," Dadullah Qane, a member of the provincial council, told Al Jazeera.

"If they are not fought back, the district will be taken over entirely."

A senior official in the province said that reinforcements have reached the area in a bid to push back the fighters.

"There were about 300 fighters that attacked the headquarters early this morning, but security forces are now fighting them back and we are hoping that the area will be cleared off soon," Farid Bakhtawar, head of the provincial council, told Al Jazeera.

Taliban claim responsibility

The Taliban immediately claimed responsibility saying the district is now under their control.

No civilian casualties have been reported so far in the attack, which comes a day after the Taliban killed seven members of the army and eight policemen in Bala Buluk district in the province.

Officials say the fighters have stepped up attacks against Afghan security forces in the province, which has often come under deadly attacks.

The province is a centre of opium cultivation and poppy farmers are often taxed by the Taliban to help fund their fight against security forces.

According to a recent BBC study, the Taliban are active in 70 percent of districts, fully controlling four percent of the country and demonstrating an open physical presence in another 66 percent.

In February, the Special Inspector General for Afghanistan Reconstruction, or SIGAR, said the Pentagon had restricted the release of information on the areas that are under the Taliban and the Afghan government.

John Sopko, who leads the independent watchdog, wrote in SIGAR's latest quarterly report that the request to classify more information was "troubling".

The US military later defended the decision, saying a "human error in labeling" caused it to classify the report.